People who believe that willpower is not limited exhibit higher self-regulation and well-being than people who believe that willpower is a limited resource. So far, only little is known about the antecedents of people’s beliefs about willpower. Three studies examine whether autonomous goal striving promotes the endorsement of a nonlimited belief and whether this relationship is mediated by vitality, the feeling of being awake and energetic. Study 1 ( n = 208) showed that autonomous goal striving predicts a change in willpower beliefs over 4 months and that this change is mediated by vitality. Study 2 ( n = 92) replicated this finding using experience sampling assessments of vitality. Experimental Study 3 ( n = 243) showed that inducing an autonomous mind-set enhances people’s endorsement of a nonlimited belief by fostering vitality. The studies support the idea that what people believe about willpower depends, at least in part, on recent experiences with tasks as being energizing or draining.